The invention relates to an illumination system for a projector, and more particularly, relates to an illumination system with a specific gobo for a projector.
Projector is one of the essential apparatus in the office. At present, the popular LCD projector has become the main stream of the new type of projector. Generally speaking, the projector structure of the prior art is composed of three partsxe2x80x94an illumination system, a color management system (CMS) and a projection system. The illumination system includes a light source of a projection-type projector and a light-converging system. The CMS separates an incident light beam into a plurality of light beams each corresponding to a specific color or polarization state. Finally, the CMS combines all the light beams to transmit into the projection system. The projection system utilizes the incident light beam to project an image.
Generally speaking, the light distribution transmitted from a good light source has to be uniform; that is, its original light beams must be as parallel as possible, so as to reduce the stray light transmitted into the CMS. As far as the image effect of the prior art is concerned, since the stray light beams will seriously affect the color purity and contrast effect of the projection image in the projection system, these stray lights from the illumination system and the CMS are regarded as the key factor for determining the quality of the image projection. In the light of an LCD projector, the conventional light-converging system makes light distribution uniform and transforms the circular light distribution of the original light beam from the light source into a rectangular light distribution of an LCD panel. Currently, the common light-converging system includes a lens array that can change the light beams from a light source into a point light source array. In the meantime, this point light source array is superimposed and output to the CMS such that the light beams transmitted into the CMS possesses the characteristic of uniformity.
The illumination system of the present LCD projector needs to use a bulb with high wattage due to the demand of high illumination. The high illumination light source generates a large amount of heat in the color management system; thereby, it""s apt to damage the optical components and LCD panels. As a result, the damage may shorten the life of the optical components, and the optical characteristic may be lowered accordingly.
FIG. 1 is a schematic view of the stray light beams generated by the wide-angle light beams according to the illumination system of the prior art of the projector. As shown in FIG. 1, the illumination system of the conventional projector includes a light source 10, two lens arrays 11 and 12 and a P-S converter 13. Besides, the conventional projector also includes a color management system 14, wherein a lens 141 receives light beams transmitted from the illumination system. The P-S converter polarizes the light beams output from the lens array 11 and 12, for instance, to transform the incident non-polarized light beam into a polarized light beam in S-state and output it to the color management system. Since the light beams originated from the light source is not completely parallel and have wide-angle components after being output from the lens array 11 and 12, they form stray light beams incident to the color management system 14 after passing through the P-S converter. Moreover, due to the imperfect focus of the lens array 11, the light beam output from the P-S converter 12 do not transform into an S-state polarization beam completely. An increase of non-parallel light beams may also deteriorate the condition that these non-S-state or non-P-state polarization beams are produced due to the incomplete polarization. The above-mentioned stray light beams are subjected to reflection and transmission for several times in the CMS system, and finally form a portion of projecting image. Consequently, the stray light beams greatly affect the chromatic purity and contrast effect of the projection image.
An object of the invention is to provide an illumination system for a projector that can overcome the disadvantage of excessive high illumination of the light source and enhance the contrast effect of the projection image. To attain this object, the invention provides an illumination system having a color management system (CMS). The illumination system includes a light source, a light-converging system, a P-S converter, and a gobo. The light-converging system is for converging the light beam coming from the light source. The P-S converter is for receiving and polarizing the light beams from the light-converging system and then transmitting the light beams into the CMS. The gobo is formed with a plurality of apertures and is provided between the light-converging system and the P-S converter. In this way, the gobo can diminish the stray light beam transmitting into the CMS. Moreover, the illumination system can prolong the service life of components and maintain the optical characteristic, and enhance the contrast effect of the projection image in the projector.